5.2.6.1 The choice and testing
of materials used in piping systems should comply with the requirements
of chapter 6 taking into account the minimum
design temperature. However, some relaxation may be permitted in the
quality of material of open-ended vent piping, provided the temperature
of the cargo at the pressure relief valve setting is -55°C or
greater and provided no liquid discharge to the vent piping can occur.
Similar relaxations may be permitted under the same temperature conditions
to open-ended piping inside cargo tanks, excluding discharge piping
and all piping inside membrane and semi-membrane tanks.
5.2.6.2 Materials having
a melting point below 925°C should not be used for piping outside
the cargo tanks except for short lengths of pipes attached to the
cargo tanks, in which case fire-resisting insulation should be provided.